Thermomechanical properties of alumina-filled plasticized polylactic acid: Effect of alumina loading percentage

Polylactic acid (PLA) is one of the most widely studied renewable and biodegradable polyesters and is expected to replace petrochemical-based synthetic polymers. In this study, we investigated the effect of the alumina volume fraction on the thermal and mechanical properties of polyethylene glycol (PEG)-plasticized PLA. The alumina particles were treated with maleic acid to improve their interaction with the PLA matrix. The field-emission scanning electron microscopy results revealed that the addition of alumina eliminated voids, leading to improved interfacial interactions between the PLA and alumina particles. The thermal conductivity of the neat PLA increased from 0.278 to 0.66?wm^?1 k^?1 with the addition of 30% alumina, which accounts for 137% increase. The tensile strength and Young's modulus of the neat PLA dropped by 52% and 56%, respectively, on the addition of 15% PEG plasticizer. However, the elongation at break increased from 5.4% to 207%, which was associated with a drop on the glass transition temperature values. The dynamic mechanical analysis results showed a drop in the storage modulus and height of the tan δ peak, revealing the increased flexibility of the composite after the inclusion of the plasticizer. The addition of 30% alumina exhibited a 41.6% increase on the stiffness of the PEG-blended PLA.     

Enhanced thermoelectric performance by alcoholic solvents effects in highly conductive benzenesulfonate‐doped poly(3,4‐ethylenedioxythiophene)/graphene composites

Benzenesulfonate‐doped poly(3,4‐ethylenedioxythiophene) (PEDOT‐Bzs)/graphene thermoelectric (TE) composites with various graphene filler contents were synthesized in five different kinds of solvents. Dodecylbenzenesulfonic acid (DBSA) was used to achieve good dispersion of graphene into the PEDOT matrix. Among the synthesized PEDOT materials, the one synthesized in methanol (PEDOT‐MeOH) had the highest electrical conductivity. X‐ray photoelectron spectroscopy (XPS) analysis showed almost the same charge carrier concentration for all PEDOT materials. However, the X‐ray diffraction (XRD) analysis highlighted the enhancement of PEDOT chain stacking by shorter‐chain alcoholic solvents, as a result of which the carrier mobility and electrical conductivity were increased. The electrical conductivity and the Seebeck coefficient of the PEDOT/graphene composites were significantly improved with increasing the graphene content, which strongly depended on increased carrier mobility. The thermal conductivity of the composites exhibited relatively small changes, attributed to phonon scattering effects. The maximum TE efficiency of the PEDOT‐MeOH/graphene composite with 75 wt % graphene showed a substantially improved value of 1.9 × 10^?2, higher than that of the other PEDOT/graphene composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42107.     

Enhancement of electrical and thermal conductivities of a polysiloxane/metal complex with metal oxides

Block copolymer‐type polysiloxane was synthesized to investigate the influence of metal oxide addition on the dispersity of metal particles in a polysiloxane/metal composite. The metal oxide was introduced in a newly synthesized polysiloxane to improve the electrical and thermal conductivities of the polysiloxane/metal composite. The composite containing the metal oxide showed better dispersion than the composite without the metal oxide. The electrical conductivity displayed a typical percolation threshold behavior. The composite containing the metal oxide showed a slightly lower critical concentration (φ_c) than the composite without. The thermal conductivity of the composite increased considerably with the concentration of the filler. Thermal conductivity was used to calculate thermal interconnectivity, and the composite containing metal oxide showed an enhanced thermal interconnectivity. POLYM. COMPOS., 31:1669–1677, 2010. © 2010 Society of Plastics Engineers.     

Flexible and high thermal conductivity thin films based on polymer: Aminated multi-walled carbon nanotubes/micro-aluminum nitride hybrid composites

Multi-walled carbon nanotubes functionalized with amino groups (MWCNT-NH₂) were prepared via the chemical modification of the carboxyl groups introduced on the surface of MWCNT. The synthesized materials and untreated micro-aluminum nitride (micro-AlN) particles were embedded in a polymer resin, viz. epoxy-terminated dimethyl siloxane. The thermal diffusivity and conductivity of all of the composites continuously improved with increasing the content of fillers. A thermal conductivity of 3.81 W/mK was achieved at an MWCNT-NH₂ loading of 3 wt% and micro-AlN loading of 70 wt% while their flexibility was maintained. This result is due to the high aspect ratio of the MWCNT-NH₂ which allows a heat conductive percolation network to be established between the micro-AlN particles. Also, all of the composites fabricated by the optimized process endured about 200,000 bending cycles without rupturing or losing their thermal conductivity.     

Enhancement of thermal and mechanical properties of flexible graphene oxide/carbon nanotube hybrid films though direct covalent bonding

The thermal conductivity and mechanical properties of graphene oxide/multiwalled carbon nanotube (GO/MWCNT) hybrid films with and without covalent bonding were examined. Chlorinated GO and amino-functionalized MWCNT were bonded covalently to fabricate chemically bonded GO/MWCNT hybrid films. Mixtures of surface-modified GO and MWCNT were filtered and then subjected to hot-pressing to fabricate stacked films. Examination of these chemically bonded hybrid films revealed higher thermal conductivity than in physically bonded hybrid films, because of the synergetic interaction of functional groups in GO and MWCNT in the films. However, the addition of excess MWCNT to the films led to an increased phonon scattering density and a decreased thermal conductivity. The hybrid films fabricated by the optimized process endured about 20000 bending cycles without rupturing or losing their thermal conductivity. The mechanical properties showed enhanced performance after increased MWCNT loading at elevated temperature due to the reinforcement effect of the MWCNT between GO layers.     

Characteristics of solderable electrically conductive adhesives (ECAs) for electronic packaging

This study investigated the effect of the viscosity of the ECAs using a low-melting-point alloy (LMPA) filler on its bonding characteristics. The curing behaviors of the ECAs were determined using Differential Scanning Calorimetry (DSC), and ECA temperature-dependant viscosity characteristics were observed using a torsional parallel rheometer. The wetting test was conducted to investigate the reduction capability of ECAs and the flow-coalescence-wetting behavior of the LMPAs in ECAs. Electrical and mechanical properties were determined and compared to those with commercial ECAs and eutectic tin/lead (Sn/Pb) solder. In the metallurgically interconnected Quad Flat Package (QFP) joint, a typical scallop-type Cu–Sn intermetallic compound (IMC) layer formed at the upper SnBi/Cu interface after curing process. On the other hand, a (Cu, Ni)₆Sn₅ IMC layer formed on the SnBi/ENIG interface. In addition, the fracture surface exhibited by cleavage fracture mode and the fracture was propagated along the Cu–Sn IMC/SnBi interface. The extremely low-level viscosity of ECAs had a significant influence on the flow-coalescence-wetting behavior of the LMPAs in ECAs and also on the interconnection properties. Stable interconnected assemblies showed good electrical and mechanical properties.     

Thermal and electrical conductivity of Al(OH)<Subscript>3</Subscript> covered graphene oxide nanosheet/epoxy composites

Al(OH)₃ functionalized graphene composites (Al–GO) were prepared using a simple sol–gel method. In this protocol, graphene oxide (GO) was prepared according to the Hummers method and functionalized to enhance its reactivity with aluminum isopropoxide by a LiAlH₄ treatment. The functionalized graphene sheets were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. These analyses confirmed that GO had been fabricated and the Al(OH)₃ layer could have a homogeneous distribution with large and dense coverage onto GO sheets. In addition, the thermal and electrical conductivity of the epoxy composites with GO and Al–GO fillers were measured. The thermal conductivities of the composites with graphene-based fillers were enhanced by the addition of fillers. In particular, the thermal conductivity of GO/epoxy composite containing 3 wt% was approximately two times higher than that of pure epoxy resin. In addition, the electrical conductivity of Al–GO embedded composites degenerated compared to GO composites.     

Oxygen‐Vacancy‐Introduced BaSnO3−δ Photoanodes with Tunable Band Structures for Efficient Solar‐Driven Water Splitting

To achieve excellent photoelectrochemical water‐splitting activity, photoanode materials with high light absorption and good charge‐separation efficiency are essential. One effective strategy for the production of materials satisfying these requirements is to adjust their band structure and corresponding bandgap energy by introducing oxygen vacancies. A simple chemical reduction method that can systematically generate oxygen vacancies in barium stannate (BaSnO₃ (BSO)) crystal is introduced, which thus allows for precise control of the bandgap energy. A BSO photoanode with optimum oxygen‐vacancy concentration (8.7%) exhibits high light‐absorption and good charge‐separation capabilities. After deposition of FeOOH/NiOOH oxygen evolution cocatalysts on its surface, this photoanode shows a remarkable photocurrent density of 7.32 mA cm^?2 at a potential of 1.23 V versus a reversible hydrogen electrode under AM1.5G simulated sunlight. Moreover, a tandem device constructed with a perovskite solar cell exhibits an operating photocurrent density of 6.84 mA cm^?2 and stable gas production with an average solar‐to‐hydrogen conversion efficiency of 7.92% for 100 h, thus functioning as an outstanding unbiased water‐splitting system.     

Development of an SH-SAW sensor for the detection of DNA hybridization

We have developed SH (shear horizontal) surface acoustic wave (SAW) sensors for the detection of DNA (deoxyribonucleic acid) hybridization on the gold-coated delay line of transverse SAW devices. DNA hybridization experiments were performed with 15-mer oligonucleotides (probe and complementary target DNA). The sensor consists of twin SAW delay line oscillators (sensing channel and reference channel) operating at 100 MHz fabricated on 36° rotated Y-cut X-propagation LiTaO₃ piezoelectric single crystals. The relative change in the frequency of the two oscillators was monitored to detect hybridization between the target DNA and probe DNA immobilized on the delay line of the SAW sensor. The measurement results showed a good response of the sensor to the mass loading effects of the DNA hybridization with a sensitivity level up to 1.55 ng/ml/Hz.     

Enhancement of the thermal conductivity of aluminum oxide–epoxy terminated poly(dimethyl siloxane) with a metal oxide containing polysiloxane

Aluminum oxide containing poly(dimethyl-methylvinyl)siloxane (PMDMS:Al₂O₃) was synthesized and blended with epoxy-terminated dimethylsiloxane (ETDS) to fabricate a thermally conducting composite. PMDMS:Al₂O₃ was added to provide interfacial interactions between the Al₂O₃ and polymer matrix. The PMDMS:Al₂O₃ containing composites revealed more enhanced thermal conduction properties because of the strengthened interfacial bonding at a fixed filler concentration. The conductivity as a function of the filler concentration was correlated with Agari’s models. Based on the coefficient obtained from Agari’s model, PMDMS:Al₂O₃ affected the formation of the conducting path in the composite. The results indicated that the presence of PMDMS:Al₂O₃ would help to establish a conducting path compared to compounds without it. All composites showed a decrease in thermal conductivity with increasing operating temperature. As expected, the PMDMS:Al₂O₃ containing composite (P-ETDS/Al₂O₃) showed more enhanced thermal conductivity than those without, regardless of the operating temperature.